Most liquid products, until fairly recently, have been machine-loaded into cans and jars using gravity, rotary, or vacuum methods. All of these methods exhibit certain speed limitations in the loading operation. In response to this problem, the positive displacement filling machine was developed, and to a certain extent has proved quite successful. The positive displacement approach calls for a device, generally using a reciprocating piston assembly, capable of rapid-fire injection of predetermined amounts of the product into storage containers.
The early positive displacement machines, such as the apparatus disclosed in my U.S. Pat. No. 3,358,719 issued Dec. 19, 1967, were designed primarily to load liquid products of a heavier nature, ranging from paste-like products to medium viscosity fluids containing solid particles. While these products proved viscous enough to permit earlier designs to operate without a special nozzle apparatus, the low viscosity, water-thin products posed special problems.
Contaminating product drip between load bursts and irregularities in fill quantities plagued low viscosity fluid loading operations. These problems were especially evident if the filling machine slowed in operating speed or stopped entirely during loading. Without secondary valve means to inhibit unwanted discharge flow, the water liquid would drain from the metering pocket faster than the displacing piston could pump it out, and overfill the container. The low viscosity fluid also collected upon the nozzle surface and occasionally dripped onto the upper sealing edge of the cans, contaminating the entire contents.
The patent to Kerr, U.S. Pat. No. 3,096,914 represents an attempt to provide a secondary valve means designed to solve the aforementioned difficulties. The design is deficient in that it relies on the presence of a partial vacuum above the diaphragm to form a proper seal against leakage.
In short, the resiliency of the diaphragm itself is not sufficient to form an effective seal during all phases of the loading cycle. For example, if the machine were slowed or stopped during the downward, compression stroke of the piston, the pressure above the diaphragm would naturally exeed the atmospheric pressure. Using a secondary valve constructed in accordance with the Kerr design, a positive seal against dribble or leak could not exist under such conditions.
The invention disclosed herein, while using diaphragm construction in its valve mechanism, is designed to provide a complete seal against undesirable leakage during all phases of the loading cycle. Extremely resilient diaphragm construction cooperates with a unique nozzle design, resulting in a pressure-actuated valve which overcomes the deficiencies inherent in known prior art.